Deformation of cellular polymeric films

Cellular films may be produced through evaporation of aqueous dispersions containing polymeric particles. The membranes of the cells are made of hydrophilic polymers which cover the particle surfaces; they form a periodic structure which separates the hydrophobic particle cores. These films are used to make adhesive coatings; in such applications, the main properties are the permeability of the film to water vapor, its mechanical resistance, and especially its resistance in wet environments. In this work, latex films have been submitted to uniaxial stretching, and the microscopic deformations of the array of membranes have been observed through small angle neutron scattering. Some films have been stretched in the dry state at a temperature above their glass transition temperature. In this case, we have found that the array of membranes was stretched uniformly according to the macroscopic deformation of the sample. Other films have been stretched in the wet state, after the membrane array was swollen with water. In this case, we have found a loss of correlation in the direction perpendicular to the stretching, indicating that the macroscopic stretching causes microscopic shear deformations.